The visual limitation in keratoconus could be explained by different alterations that occur in these corneas and allowed development of a new grading system for this condition.

Objective: To evaluate the changes in correlations of higher order aberrations of the first corneal surface with halo phenomena, a form of image degradation, under night vision conditions measured objectively after successful LASIK (laser in situ keratomileusis) surgery. Methods: A prospective, observational, analytical study of 110 eyes that had undergone successful LASIK surgery for myopia and astigmatism. Preoperative sphere was (mean (SD)) 23.48 (1.70) D (0 to 28.00 D) and preoperative cylinder was 20.86 (0.87) D (0 to 24.00 D). Visual disturbance caused by halo phenomena was measured with the Starlights v1.0, and pupil size was measured with Colvard pupilometry after adaptation to a dark environment (0.17 lux). Corneal aberrations were computed for a corneal diameter representative of the eye's entrance pupil under night vision conditions. Results: The halo disturbance index increased in this study by a factor of 2.15 after successful LASIK surgery. Total root mean square for monochromatic higher order aberration displayed a significant correlation with halo disturbance index (r = 0.42; p,0.01). However, only secondary astigmatism (r = 0.36; p,0.01), coma (r = 0.25; p = 0.02) and spherical aberration (r = 0.40; p,0.01) were responsible for such behaviour, with the remaining corneal aberrations up to the sixth order not displaying any significant correlation when considered individually. Conclusion: Patients undergoing LASIK procedures display an increase of halo phenomena around lights in night vision conditions, even when the results of the surgery are considered entirely satisfactory according to current international standards of predictability, efficacy and safety. Secondary astigmatism, coma and spherical aberration are the higher order aberrations up to the sixth order that significantly correlated with halo disturbance index.

We present a simple device (called a halometer) to detect and quantify the phenomenon of halos after certain surgical procedures, such as refractive surgery. The task of the subject consists basically of discriminating, after dark adaptation, a small light source around a central high-luminance stimulus. The device, which is connected to a computer, provides a disturbance index to measure the effect of halos on the observer's vision. Tested with normal subjects and patients after LASIK (laser in situ keratomileusis) surgery, this apparatus proved sufficiently sensitive to quantify the halos in subjects who had undergone surgery.

Monovision correction by LASIK improved functional near vision in presbyopic patients. Although visual acuity was good for far vision, contrast sensitivity and stereoacuity diminished significantly.

A high correlation was found between the Strehl ratio and the disturbance index in patients who underwent LASIK, regardless of the ablation algorithm applied. Optical and visual deterioration were greater after standard ablation.